Generators having a rotor carrying permanent magnets are known. They are generally deemed to be reliable and require less maintenance than other generator topologies.
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft either directly drives the generator rotor (“directly driven”) or through the use of a gearbox. For offshore wind turbines, direct drive systems employing permanent magnets are usually chosen.
Such a direct drive wind turbine generator may have e.g. a diameter of 6-8 meters and a length of e.g. 2-3 meters. Hundreds of magnets may need to be screwed or glued to the circumference of the rotor. It will be clear that this manufacturing process can be cumbersome.
Furthermore, if one or more magnets is damaged and needs to be replaced, the access to these magnets can be complicated (especially with large size generators), such that maintenance can become very expensive.
This size and type of generator is not limited to the technical field of wind turbines only. Generators of considerable dimensions may also be found e.g. in steam turbines and water turbines.